Sewage treatment method and apparatus



Dec. 21, 1943. p M THAYER 2,337,507

SEWAGE TREATMENT MTHOD AND APPARATUS Filed Aug. s, 1940 @en 2li, i943 OFFICE ssi/vaas TREATMENT Mn'rnon AND serres This invention relates to sewage treatment method and apparatus in which sludge removed from the sewage in a settlement tank is classitied in a separa chamber from that in which it is originally settled, the heavy part of the sludge being conducted to a sludge digestion chamber and the lighter part being returned to and mixed with the incoming sewage.

ln accordance with my invention, the type of sewage sludge `which passes to the digestion tank and that which returns to the aeration tank, are separated in accordance with their virility. The most active sludge and that which is capable of retaining its activity under adverse conditions remains relatively light even after standing for a considerabie time in contact with less virile sludge, and, therefore, by a second settling operation, is removable from the vupper part of a. second settlement tank while the thickened sludge, more suitable for digestion, is removable from the bottom of such tank.

.ii/ly invention is illustrated diagrammatically in the accompanying drawing, which represents a sewage treatment and sludge digesting plant in its essentials.

in the illustrated embodiment of my invention, raw sewage is delivered to a comminutor 2 which reduces all oi the sewage solids to a size that they will readily circulate with the liquid become converted either into digestible solids or useful activated sludge.

From the comminutor 2, the liquid and'solids Tiow together through a conduit 3 to an aeration tank 5, previously activated classied sludge being admitted to the conduit 3 at the junction and owing with the raw sewage into the aeration tank Si. v

The aeration tank E may be of any type suitfo er the activated sludge process. As here it comprises a vertical centrally located sludge and provided with a deilector -ie tcp which spreads the sewage and sludge mushroom shaped violent rain over the en- .Liace of the liquid in the tank 5. The w of the material in the tubular member 6 is caused by a screw propeller, not shown, driven motor lil axially mounted above the tubular -ber The dow of sewage and sludge is s ciently rapid that even the heavy sludge is in circulation with the liquid up the tube own the entire area of the tank, vand across door to the entrance of the tube t. The tank s made oi such size that the average ratention period for the sewage is from two to six hours, this being a suicient time with the character of sludge provided by my improved method and apparatus thoroughly to oxidize the sewage and flocculate the sludge.

A conduit I2 leads from the level of the liquid surface in the tank 5 to an inlet ring I3 centrally located in a settling tank I4. The ring I3 prevents the lnowing sewage and sludge from creating an agitation of the liquid and sludge in the settling tank, and permits the mixed material to flow gently out of the bottom of the ring, from which it spreads somewhat evenly over the area of the tank. The sludge, both heavy and light, eventually settles to the bottom of the tank, and the clear liquid ows upwardly through the screen I5 and to the outfalI through overflow pipe I6. The screen I5 is kept free of clogging particles by the periodic backow of clear liquid forced downwardly through the screen by the traveling nozzle device I8. It will be understood that the sewage and sludge owlng to the settling tank from the aeration tank is a mixture of sludges, some of which have been treated only a Very short time in the aeration tank, and some of which have remained in the tank for a period much longer than the average, and of all intermediately treated sludges, and in addition, of sludge which has passed through the aeration tank not only once, but many times before.

All of these various kinds of sludges are either immediately or later of sufficient gravity to settle to the bottom of the settling tank. Such sludges as are at rst light enough to iioat are prevented from passing out with the effluent by the screen l5, and eventually give 01T their gases and settle to the bottom of the settling tank. I,

All of the mixture of sludges which settles upon the bottom of the settling tank I4 is gradually scraped to the middle of the tank and into the sump I9 by the traveling scraping blades 2li, which are slowly moved around the tank by power means 2i.

All of the material, which includes both sewage solids and several kinds of sewage sludges, iiows together through the conduit 22 into the classification tank 23, which must be of such a s'ize that a the incoming sludge maintains a slight degree ofv agitation within the tank. Here the really heavy sludges sink immediately to the bottom and pass at a regulated rate to the digestion tank 25, where digestion takes place in the usual manner but without interference from the very active aerobic bacterial matter which, by my invention.

is largely separated from the more readily digestible sludge in the classifier 23,

The highly aerobic bacterial sludges forming a part of the mixture of sludges in the classier 23 are lighter than the other sludges, and therefore become stratied in the upper portion of the classication tank 23, and pumped by means of the pump 21 back into the junction 4 with the conduit 3,

By the use of my method and apparatus, sewage treatment plants may be operated more economically than if the sludge returned to the aeration tank from the settling tank is made up of either a conglomerate of the sludges settled in the aeration tank or of classifedsludge made immediatelyafter the materialhas arriiged in the main settling tank and before some of the absorbed or attached gases have been discharged from the sludge.-

It is to Vbe understood that the apparatus of this disclosure may be varied without departing from the scope of my invention and that the terial activated sludge to become partially anaerobic by standing in the bottom of a settling tank in contact with other anaerobic bacterial sludge, removing the mixture of such sludges and .subjecting them to gravity classification, transfrom the bottom of the 'clays,siiication tank, and

method may be carried out with a large variety y of known devices.

I claim 1. That method of sewage treatment,` bylitl'ie* activated sludge process which comprises settlingl 'f all ofthe sludge from the aeration tankinva.- settling tank and thereafter classifying-by gra, ity the sludge from the settling tank, returning the lighter part of the sludge toithezaerationy the heavier; partv fjfthejx.-

tank and disposing of sludge.

2. That method of 'sewage'Yftreatn'i'ent4 y and,`

sludge disposal which comprises-continuously aerating the incoming Vsewage at one; location in the presence of its own and-previously pre.'- pared sludge, Continuouslysettlingtheiudge location, conti uously y f from the liquid at a 'secon A discharging separated-cla ifiedliiiuid a from said secondflocation,continuously gently agitating the sludge ata.' third location, ously separating the heavy f 'from theiligh at said third -xlocatiod'and continuous light sludgeto an ing raw sewage."` i mi 4. The method of sewage treatment'andv sludge to maintatin the flow of sludgethrough all of f a connection between the yupper part of the classification tank-"tofconduct the light sludge to the aeration ta'nkj.

6. Inv a sludge disposal-system, a sludge settling tank1,a'. sludgeclasslfying tank, a conduit .1'extending-ffrorn thebottom o'f the sludge settling tankltothe-sludge' Yclassifying tank, a sludge glrdi'gestingtank; a conduit extending from the botl"tvornmofj vsaid classifying tank to said digesting titank,l aniaerating tank, a conduit extending from 'fa hi'gh'flevel in said classifying tank to said aerating tank, a conduit extending from said aerating tank to said settling tank. and means said conduits.v

- 'lqIna sludge disposalsystem, an aeratingl f' tank, a l*sludge settlingv tank connectedv to said aerating-tank,tolreceivel all the sludge and liqj-uid therefrom, a'sldge classifying tankconnected -to'sai'd settlingv tankv to receive all the -settled sludge from thelatter,` Va, connection from thev upperfpa'rlt, of s'a'id vclassifying tank to Isaid aeratingtankfto conduct light sludge to the latf `tei-,1,aridgan' outlet-at the bottom of said classifykv-"for',V disposing of heavysludge there- "8.;' In an 'activated sludge disposal system of AQ*tleutyp'e'comprisingan'aeration tank, the vcomfbination. including, 'af-settling tank supplied with tliegjsludgeand liquid from ,the aeration tank, 1, -aisludgeclassifyingrtank' connected to the set- :ftling tank; and receiving all the settled sludge from y,the settling tank, means for returning to rtheaerai'sion'tank light sludge Vfrom the upper jpxalitof' the classifying tank, and'means for With- 'drawing.and disposing of the heavy sludge colthe classifying tank.

PAUL M. THAYER. 

